GIFT 
DEC  8    1915 


CONCRETING  IN  WINTER 


PUBLISHED  BY  THE 


ASSOCIATION  OF  AMERICAN  ^PORTLAND 
MANUFACTURERS 


BELLEVUE  COURT  BUILDING,  PHILADELPHIA 


A  REQUEST   TO   THE 
READER 

FREE    HELP 


HOULD  you  find  this  bulletin  helpful  in  building 
with  concrete,  we  would  consider  it  a  favor  to 
have  you  so  inform  us.  Likewise,  we  would 
appreciate  a  description  (and  a  photograph,  if  possible) 
of  what  you  have  built.  In  this  way  you  will  assist  us 
in  aiding  others  in  the  same  way  we  trust  we  have 
helped  you. 

If  you  do  not  fully  understand  any  part  of  this 
book,  or  if  you  desire  further  information,  we  would  be 
glad  to  have  you  write  to  the 

ASSOCIATION  OF 
AMERICAN  PORTLAND  CEMENT  MANUFACTURERS 

BELLEVUE    COURT  BUILDING,  PHILADELPHIA,  PA. 


CONCRETING  IN 
WINTER 


PUBLISHED  BY  THE 

ASSOCIATION  OF  AMERICAN  PORTLAND 
CEMENT  MANUFACTURERS 

BELLEVUE  COURT  BUILDING,  PHILADELPHIA,  PA. 


P73 


COPYKIGHT,  1915 
BY  THE  ASSOCIATION  OF  AMERICAN  PORTLAND  CEMENT  MANUFACTURERS 


Concreting  in  Winter 


ONLY  a  few  years  ago  building  construction  necessitating  concrete 
work  was,  by  common  consent,  stopped  on  the  approach  of  cold 
weather. 

But  many  large  contracting  companies,  who  have  carried  on  their  con- 
crete work  uninterruptedly  with  results  as  satisfactory  as  obtained  during 
more  favorable  weather  conditions,  have  proved  that  concreting  is  possible 
during  periods  of  freezing  weather  if  proper,  simple  precautions  are  taken. 
A  knowledge  of  this  has  made  the  subject  of  concrete  construction  in 
winter  of  general  interest  to  many  users  of  cement;  in  fact,  since  it  is  a 
slack  season  many  have  found  winter  the  best  time  of  year  for  them  to 
build  with  concrete.  However,  successful  results  depend  upon  exercising 
certain  additional  precautions  beyond  those  that  must  be  observed  during 
other  seasons  of  the  year.  The  object  of  this  publication  is  to  describe 
methods  that  should  be  followed  to  insure  success  in  concreting  carried  on 
during  cold  weather. 

Advantages 

Contractors  were  probably  the  first  to  recognize  the  advantages  resulting 
from  being  able  to  continue  concreting  without  interruption  during  the 
winter.  Tools  and  machinery  were  thus  kept  employed  instead  of  being 
idle  for  three  or  four  months.  Overhead  expenses  and  depreciation,  being 
distributed  over  the  cost  of  a  greater  volume  of  work,  were  considerably 
reduced.  Capable  and  faithful  employees,  developed  into  an  efficient 
organization,  were  retained  for  more  active  service  in  the  spring. 

With  the  possibility  of  carrying  on  work  during  the  winter,  these 
troubles  are  largely  eliminated.  Materials  can  be  promptly  delivered  be- 
cause railroads  and  supply  houses  are,  as  a  rule,  not  so  rushed  during  the 
winter  as  in  the  summer  when  all  building  operations  are  active.  Another 
decided  advantage  is  that  the  owner  need  not  suffer  any  delay  in  the  com- 
pletion of  the  work,  consequently  can  utilize  his  buildings  in  the  usually 
more  active  spring  and  summer  seasons. 

Disadvantages 

If  such  precautions  as  will  be  described  later  are  followed,  probably  there 
is  but  one  disadvantage  to  carrying  on  concrete  work  during  freezing 
temperatures — that  is  the  slightly  increased  cost  of  the  resulting  construe- 

M17471 


tion.  This  comes  from  the  expense  involved  in  applying  necessary  pre- 
cautions and  from  the  slightly  reduced  efficiency  of  workmen  when  more 
or  less  exposed  to  the  elements.  Although  this  increased  cost  may  be  from 
6  to  10  per  cent,  perhaps  greater,  it  rarely  exceeds  the  latter  figure;  and 
when  early  occupancy  of  a  structure  is  the  essential  reason  for  carrying 
on  the  work  time  saved  usually  more  than  offsets  any  increase  in  cost. 

Freezing  of  Concrete  Must  be  Prevented 

Although  claims  are  sometimes  made  that  concrete  frozen  before  hardening 
may  not  suffer  permanent  injury  if  upon  thawing  it  is  not  again  exposed 


FIG.  1. — HEATED  WATER  BEING  DISCHARGED  DIRECTLY  INTO  MIXER. 


to  freezing  weather  until  sufficiently  hardened  to  be  unaffected  by  such 
exposure,  nevertheless  every  precaution  should  be  taken  to  prevent  freez- 
ing. If  this  is  guarded  against  for  at  least  five  days,  the  danger  of  injury 
from  subsequent  freezing  may  be  assumed  to  have  passed. 

To  insure  that  concrete  will  have  sufficient  heat  to  assist  in  hastening 
early  hardening,  materials  and  water  should  be  heated  so  that  the  concrete 
when  deposited  will  have  a  temperature  not  lower  than  80  degrees  Fahren- 
heit. Heat  given  to  concrete  by  heated  water  and  heated  sand  and  gravel 

4 


or  broken  stone,  and  afterward  maintained  by  proper  protection  when  the 
concrete  has  been  deposited,  is  increased  by  heat  developed  within  the 
concrete  during  the  period  of  early  hardening  of  the  cement.  Not  only 
does  the  heating  of  aggregates  and  water  hasten  the  development  of  this 
internal  heat,  but  the  temperature  of  the  concrete  is  increased  somewhat 
above  that  prevailing  when  concrete  is  deposited  under  the  usual  summer 
weather  conditions;  and  these  factors  combined  help  to  maintain  the 
temperature  of  the  freshly  deposited  concrete  above  freezing. 

Properly  hardened  concrete  and  frozen  concrete  often  look  alike  on 
casual  inspection.  For  this  reason  extreme  care  must  be  taken  when  re- 
moving forms  from  concrete  which  has  been  exposed  to  freezing  weather. 
Forms  must  be  left  in  place  until  the  concrete  has  obtained  sufficient 


r 


FIG.  2. — HEATING  MIXING  WATER  BY  EXHAUST  STEAM.     Note  water  tank  at  top  of 

mixer. 

strength  to  be  self-supporting  or  to  support  imposed  loads.  Frozen  con- 
crete can  be  detected  by  pouring  hot  water  on  the  surface  or  applying 
heat  from  a  painter's  or  plumber's  blow  torch.  If  the  surface  becomes 
soft  after  application  of  hot  water  or  upon  exposure  to  heat  from  a  torch, 
there  is  good  evidence  that  the  concrete  is  frozen,  and  forms  should  not  be 
removed. 

Although  concrete  is  exposed  to  greatest  danger  when  the  temperature 
is  below  freezing,  nevertheless  precautionary  measures  consisting  of  heating 
materials  and  water  should  be  taken  when  the  temperature  drops  to  40 
degrees,  because  of  the  assistance  that  this  added  heat  will  be  in  accelerat- 
ing hardening.  Such  measures  are  also  a  protection  against  a  sudden 

5 


drop  in  temperature,  which  is  quite  likely  to  occur  when  prevailing  tem- 
peratures are  as  low  as  40  degrees. 

Methods  of  Protection 

Several  methods  are  commonly  employed  to  afford  the  necessary  protection 
against  freezing  to  freshly  deposited  concrete.  In  the  following  paragraphs 
these  are  described  separately;  but  one  should  remember  that  none  of 
these  methods  is  commonly  employed  alone;  usually  they  are  combined, 
that  is,  merely  covering  freshly  deposited  concrete  placed  in  cold  forms  and 
mixed  with  unheated  materials  and  water  which  have  a  temperature  near 


FIG.  3. — HEATING  STONE  PILE  WITH  STEAM.     Canvas  covering  to  retain  all  heat  possible. 

freezing,  is  not  sufficient,  as  the  concrete  is  likely  to  freeze  at  once.  Just 
how  many  of  the  protection  methods  need  be  combined  and  used  depends 
upon  the  character  of  the  work  and  the  conditions  under  which  it  is  being 
carried  on. 

Use  of  Salt  in  Mixing  Water 

Because  cheap  and  simple  to  use,  the  practice  of  adding  common  salt  to 
the  mixing  water  was  probably  the  first  and  most  popular  method  em- 
ployed to  prevent  freezing  of  freshly  deposited  concrete.  In  present 

6 


practice,  however,  the  use  of  salt  is  declining.  Salt  simply  lowers  the 
freezing  point  of  the  mixing  water.  In  no  way  does  it  hasten  the  hardening 
of  the  concrete;  in  fact,  it  causes  the  concrete  to  harden  more  slowly. 
Furthermore,  the  result  of  using  salt  up  to  the  safe  limit  affords  protection 
against  only  a  moderate  degree  of  cold. 

Rules  for  the  use  of  salt  have  been  formulated,  the  most  widely  accepted 
one  being  that  which  called  for  its  addition  to  the  mixing  water  in  an 
amount  equal  to  one  per  cent  of  the  weight  of  the  water  for  each  degree 
of  temperature  below  freezing  point  to  be  counteracted;  and  as  not  more 
than  10  per  cent  can  safely  be  used  without  probability  of  impairing  the 


FIG.  4. — METHOD  OF  HEATING  SAND. 

strength  of  concrete,  salt  affords  protection  only  for  temperatures  above  22 
degrees;  that  is,  for  a  range  of  10  degrees  below  freezing. 

Experiments  seem  to  indicate  that  the  presence  of  salt  in  concrete  is 
particularly  objectionable  in  reinforced  construction,  inasmuch  as  corrosion 
of  the  steel  results;  and  as  this  corrosive  action  increases  as  the  percentage 
of  salt  is  raised  the  use  of  salt  is  not  to  be  recommended  in  reinforced  con- 
struction. If  used  at  all,  its*  use  should  be  confined  to  plain  mass  work 
under  conditions  where  the  temperature  is  not  likely  to  drop  more  than  a 
few  degrees  below  freezing,  and  where  the  appearance  of  the  finished  work 
will  not  be  marred  by  the  resulting  efflorescence  that  is  common  to  work 
in  which  salt  has  been  used. 


Several  other  substances  have  been  recommended  or  employed  in 
the  same  manner  that  salt  is  used  to  lower  the  freezing  point  of  concrete. 
Among  these  is  calcium  chlorid;  alcohol  and  glycerin  also  would  produce 
a  similar  action  in  lowering  the  freezing  point.  Calcium  chlorid  presents 
the  same  objections  mentioned  for  salt,  and  alcohol  and  glycerin  may  be 
considered  impractical  on  account  of  cost — while  the  general  objection  of 
lowering  the  freezing  point  without  hastening  the  hardening  of  the  concrete 
applies  to  all  of  these  materials.  In  cold  weather  the  object  to  be  attained 
is  a  hastening  of  the  hardening  action  and  this  cannot  be  accomplished 
without  heat. 


FIG.  5. — HEATING  STONE  WITH  SHEET  IRON  CYLINDERS.     Workmen  are  digging  trench 
for  placing  additional  cylinders. 

Heating  of  Materials 

This  preventive  measure  is  undoubtedly  the  most  effective  one  leading 
to  safe  and  satisfactory  results.  The  heat  given  to  the  concrete  through 
this  method  accelerates  hardening  and  early  strength  of  the  concrete, 
and  exerts  no  injurious  effect  on  the  final  strength.  If  heating  of  materials 
is  properly  done  and  the  concrete  quickly  deposited  and  protected  before 
the  added  heat  can  be  lost,  the  concrete  will  harden  almost  as  rapidly  during 
freezing  temperatures  as  at  other  times  of  the  year,  and  will  ultimately 
acquire  the  same  strength  as  if  placed  during  summer  weather. 

8 


Heating  Water 

Mixing  water  is  the  easiest  of  the  materials  to  heat.  A  temperature 
averaging  150  degrees  can  easily  be  secured  and  maintained.  Two  methods 
are  in  most  general  use  for  heating  mixing  water.  One  is  by  means  of  live 
or  exhaust  steam  from  a  boiler  plant  on  the  job,  and  the  other  is  to  heat 
the  water  in  tanks  or  kettles  over  a  fire.  On  large  jobs  heating  by  steam 
is  the  method  commonly  employed.  There  are  now  available  a  number 
of  devices  similar  to  the  ordinary  steam-boiler  injector  which  lift  and,  at 
the  same  time,  heat  the  water  by  passing  it  through  a  mixing  valve  where 
it  comes  in  contact  with  live  steam.  Two  pipes  lead  to  the  valve,  one 


Courtesy  Turner  Const.  Co. 

FIG.   6. — CONCRETE   FLOOR   COVERED   WITH   CANVAS   SUPPORTED   SHORT   DISTANCE 
ABOVE  IT.     Heat  from  salamanders  raises  temperature  of  air  in  this  space. 


carrying  steam  and  the  other  cold  water.  After  passing  through  the  valve 
the  heated  water  is  discharged  into  a  tank  usually  placed  on  the  concrete 
mixer,  or  may  be  discharged  directly  into  the  mixer  if  the  discharge  pipe 
is  equipped  with  a  measuring  valve.  (See  Fig.  1.) 

Exhaust  steam  from  the  boiler  operating  the  mixer  is  often  allowed  to 
discharge  into  a  water  tank  located  above  the  mixer,  thus  raising  the  tem- 
perature of  the  water.  (See  Fig.  2. )  Such  a  tank  is  usually  equipped  with  a 
float  mechanism  to  measure  the  correct  amount  of  water  for  each  batch  of 
concrete;  but  this  arrangement  is  often  unsatisfactory  because  not  enough 

9 


water  can  be  heated  to  the  desired  temperature  before  required  for  the  next 
batch.  In  such  cases  additional  tanks  or  barrels  must  be  provided  to 
insure  a  sufficient  supply  of  heated  water.  Exhaust  steam  is  not  so  effec- 
tive as  live  steam  because  naturally  of  lower  temperature,  neither  can  the 
supply  be  so  easily  regulated. 

Perhaps  the  method  used  to  a  greater  extent  than  any  other  is  to  install 
in  a  water-barrel  or  tank  a  steam-pipe  or  short  coil  connected  with  the 
boiler  plant  of  the  mixer.  This  arrangement  is  easily  cared  for  and  regu- 
lated, and  gives  the  best  average  results.  On  small  jobs  where  a  steam- 
power  mixer  is  not  employed,  a  tank  or  large  kettle  supported  above  a  fire 


FIG.  7. — PROTECTING  NEW-LAID  SIDEWALKS  AGAINST  POSSIBLE  DROP  IN  TEMPERATURE 

DURING  THE  NIGHT. 


may  be  used.  This  method,  however,  is  not  satisfactory  when  large 
quantities  of  mixing  water  are  required,  and  is  not  so  convenient  as  heating 
with  steam,  because  continual  attention  is  required  to  keep  a  proper  fire 
under  the  tank  or  boiler. 


Heating  Sand  and  Gravel  or  Stone 

In  freezing  weather  aggregates  contain  considerable  frost  and  sometimes 
lumps  of  snow  and  ice.  Such  frost  and  frozen  material  not  only  chill  the 
concrete,  even  though  the  water  used  may  have  been  heated,  but  also 

10 


prevent  thorough  mixing.  Therefore,  sand  and  gravel  must  be  thoroughly 
thawed  out  by  heating;  although  the  temperature  should  not  generally 
be  raised  above  150  degrees. 

Practically  the  same  methods  are  used  both  for  heating  sand  and  gravel 
or  stone.  Sometimes  the  sand  and  stone  are  heated  by  steam  by  placing  tar- 
paulins over  the  piles,  thrusting  pipes  in  the  piles  of  material  to  be  heated, 
and  turning  steam  into  the  pipes.  (See  Fig.  3.)  Another  method  consists  of 
piling  the  material  around  and  on  top  of  some  kind  of  a  furnace — usually 


Courtesy  Turner  Const.  Co. 

FIG.  8.  —  CANVAS  HOUSING  PROTECTING  FRESH  CONCRETE. 


improvised  from  a  sheet-iron  cylinder  such  as  an  old  smokestack,  a  section 
of  an  old  iron  sewer-pipe  or  culvert,  or  an  old  boiler.  (See  Fig.  4.)  A  fire  is 
built  within  and  the  aggregate  piled  around  and  above  the  stove  thus  made. 
This  is  a  very  simple  and  inexpensive  method,  and  is  employed  with  satis- 
faction upon  jobs  of  moderate  size.  There  may  be  one  disadvantage  to  this 
method  :  Unless  the  material  in  the  pile  is  constantly  turned  or  raked  over, 
the  particles  nearest  the  fire  may  be  heated  too  much  and  perhaps  injured, 
while  those  farthest  away  at  the  top  'and  sides  of  the  pile  may  be  hardly 

11 


thawed  out;   also  the  dumping  of  fresh  supplies  of  materials  is  somewhat 
hindered.     (See  Fig.  5.) 

Steam  heating  of  aggregates  is  undoubtedly  the  most  suitable  method 
when  steam  supply  is  available.  There  is  no  danger  of  overheating  and 
consequent  injury.  A  boiler  pressure  of  25  pounds  is  sufficient,  and  in 
some  cases  an  old  boiler  that  is  no  longer  safe  for  high  steam  pressure  may 
be  used.  When  the  steam  heating  method  is  employed  for  sand  and  stone, 
the  materials  may  be  heaped  on  coils  of  steam  pipe  through  which  steam 


FIG.  9.— CANVAS  HOUSING  ON  CONCRETE  GRAIN  BINS.     Space  under  canvas  kept  warm 
with  salamanders.     Concrete  mixed  by  hand  beneath  this  protection. 

circulates  or  lengths  of  pipe  with  open  ends  may  be  thrust  into  the  piles  as 
already  suggested.  In  the  latter  case  best  results  will  be  secured  if  the 
pipes  are  drilled  with  small  holes  every  18  inches,  thus  causing  the  steam 
to  be  distributed  through  a  greater  volume  of  the  pile.  Steam  pipes  when 
used  as  suggested  do  not  interfere  with  the  dumping  of  additional  supplies 
of  material  and  can  be  readily  shifted  about  as  may  be  necessary. 


12 


Heating  Cement 

Cement  being  only  a  relatively  small  portion  of  the  concrete  mass  need  not 
be  heated. 

Heating  Forms  and  Reinforcing  Steel 

All  ice  and  frost  must  be  removed  from  forms  before  placing  concrete. 
This  can  readily  be  accomplished  by  turning  a  jet  of  steam  against  the  face 
of  the  forms  which  will  not  only  remove  ice  and  frost  but  at  the  same  time 
heat  the  forms  and  reinforcing  steel.  This  is  essential  because  much  of  the 


Courtesy  Turner  Const.  Co. 

FIG.  10. — SALAMANDERS  IN  USE.    Notice  housing  in  background  covering  window  spaces. 

heat  given  to  the  concrete  by  the  heated  materials  would  be  lost  if  the 
concrete  were  deposited  in  the  cold  forms. 


Protection  of  Concrete  After  Depositing 

Concrete  mixed  with  heated  materials  and  left  unprotected  would  naturally 
soon  lose  much  of  its  heat  if  exposed  to  low  temperatures  and  might  even 
freeze  at  least  on  the  surface,  even  though  the  materials  had  been  heated. 
Although  all  concrete  must  be  protected  immediately  after  depositing  in 
freezing  weather,  some  classes  of  construction  require  more  thorough  safe- 

13 


guarding  than  others.  For  instance,  thin  floor  slabs  (see  Fig.  6),  beams, 
columns,  sidewalks  and  similar  construction  have  a  large  surface  area  in 
comparison  with  their  volume,  therefore  they  require  more  careful  protec- 
tion than  need  be  given  to  foundations,  abutments,  and  similar  mass  con- 
struction, where  the  excavation  or  bulk  of  the  mass  and  heavy  forms 
afford  part  of  the  necessary  protection. 

Floors  are  usually  protected  by  a  12-inch  layer  of  hay  or  straw.     In 
such  a  case  the  concrete  should  first  be  covered  with  building  paper  or 


FIG.  11. — SALAMANDERS  IN  USE  ON  FINISHED  FLOOR. 

canvas  before  placing  the  protective  covering,  and  in  outside  work -the 
straw  should  be  weighted  down  with  short  boards  to  prevent  the  covering 
from  being  blown  away.  Such  protective  covering  should  be  placed  with 
special  care,  particularly  where  the  concrete  is  exposed  to  unusual  condi- 
tions, as  where  the  floor  is  at  the  top  of  a  building.  Sidewalks,  also,  must 
receive  extra  care  if  successful  results  are  to  be  obtained.  (See  Fig.  7.) 
Walks  expose  a  large  surface  area  to  cold  winds  and  the  concrete  must  be 
well  covered  with  straw  or  hay,  or  else  housed  in  by  means  of  a  frame  and 

14 


canvas  covering,  and  suitable  temperature  maintained  by  steam  or  sala- 
manders. 

After  forms  are  in  place  for  the  construction  of  each  floor  of  a  building, 
the  structure  is  usually  housed  in  by  canvas  as  shown  in  Fig.  8.  Some- 
times the  canvas  is  supported  by  frames  to  oppose  resistance  to  the  wind. 
When  the  housing  is  to  be  exposed  to  high  winds  and  is  to  remain  in  place 
for  a  considerable  time,  light  sheathing  boards,  instead  of  canvas,  are  often 
used  to  enclose  the  construction.  An  ingenious  method  of  enclosing  was 
used  in  connection  with  the  building  of  the  National  Tire  and  Rubber 
Co.  at  Palestine,  Ohio.  (See  Fig.  12.)  Frames  6  feet  wide  and  14  feet 
long,  covered  with  heavy  waterproof  paper,  were  nailed  to  the  forms  and 
provided  an  easily  erected  and  tight  enclosure.  The  cost  of  this  method 
of  enclosing  as  given  in  the  Engineering  Record  for  January  9,  1915,  was 
2.1  cents  per  square  foot  in  place.  Salamanders  are  kept  burning  with- 
in the  enclosure  until  the  concrete  has  hardened  sufficiently  to  stand 
exposure  to  any  temperature.  (See  Fig.  9.) 

Salamanders  are  open,  sheet-iron,  coke-burning  pots  used  as  stoves,  and 
give  off  no  smoke.  Under  ordinary  conditions  one  salamander  is  provided  for 
each  500  square  feet  of  floor  surface.  (See  Fig.  10.)  To  maintain  the  desired 
protection,  provided  the  housing  in  of  the  structure  has  been  properly  done, 
an  average  of  150  pounds  of  coke  will  be  burned  for  each  twenty-four  hours. 
By  means  of  salamanders  the  temperature  of  an  interior  (See  Fig.  11),  when 
effectively  enclosed  by  canvas  or  sheathing,  can  easily  be  maintained  at 
about  65  degrees.  This  not  only  allows  the  concrete  to  harden  under 
practically  normal  conditions,  but  adds  considerably  to  the  comfort  of 
workmen  that  may  be  employed  in  the  building.  Salamanders  are  usually 
kept  in  operation  from  five  to  seven  days  on  each  floor.  Experience  has 
shown  that  the  cost  of  operating  them,  including  fuel  and  labor  necessary  to 
keep  fires  burning,  ranges  from  70  to  80  cents  per  day  of  twenty-four  hours. 

Removal  of  Forms 

One  other  important  precaution  should  be  observed  in  connection  with 
cold  weather  concreting:  In  spite  of  the  fact  that  materials  may  have  been 
heated  and  the  temperature  kept  as  high  as  possible,  nevertheless  it  is 
practically  impossible  to  uniformly  maintain  temperature  conditions  as  they 
normally  prevail  in  summer. 

In  connection  with  the  effect  of  low  temperatures  on  the  setting  of 
concrete,  Dr.  A.  S.  Cushman,  of  the  Institute  of  Industrial  Research,  after 
a  series  of  tests,  states:  "It  will  be  noted  that  low  temperature  and  hiqjh 
humidity  retard  the  setting  of  Portland  cement  concrete.  When  the  nor- 
mal percentage  of  water  is  increased,  the  setting  of  the  cement  is  further 
retarded,  but  where  the  normal  percentage  of  water  is  decreased,  a  curve 
is  obtained  lying  between  the  normal  percentage  of  water  at  low  tempera- 

15 


ture  and  the  normal  percentage  of  water  at  normal  temperature.  The 
points  obtained  for  this  curve,  however,  are  more  erratic  than  in  any  of  the 
other  series,  this  being  due  to  the  extreme  difficulty  of  tamping  the  dry 
concrete  uniformly  in  the  different  molds.  While  indications  point  to 
the  fact  that  a  dry  concrete  Avill  set  up  more  rapidly  under  conditions  of 
low  temperature  and  high  humidity  than  a  normally  wet  or  sloppy  con- 
crete, great  caution  should,  nevertheless,  be  exercised  to  see  that  the  con- 
crete is  made  as  dense  as  practicable." 

Concrete  deposited  during  freezing  weather  will  not  harden  as  quickly 
as  in  warm  weather;  therefore,  forms  must  be  left  in  place  longer  than  they 
would  be  allowed  to  remain  in  summer.  This  often  requires  that,  par- 


Courtesy  Engineering  Record 

FIG.  12. — USE  OF  PAPER-COVERED  FRAMES  FOR  ENCLOSING  BUILDING. 


ticularly  in  floor  construction  in  reinforced  concrete  buildings,  extra  sets 
of  forms  be  provided  to  prevent  delay  in  prosecuting  work.  Removing 
forms  at  too  early  a  period  is  to  be  condemned  in  connection  with  all  con- 
crete work,  regardless  of  weather  conditions,  but  deserves  particular 
emphasis  in  connection  with  cold  weather  work.  Any  additional  money 
that  may  be  saved  as  the  result  of  removing  forms  a  day  or  two  ahead  of 
the  safe  time  is  often  disastrously  offset  by  failures  that  could  have  been 
prevented  by  leaving  them  in  place  a  day  or  two  longer. 

If  instructions  contained  in  this  booklet  are  strictly  observed,  there 
will  be  no  danger  of  frozen  concrete  nor  any  trouble  experienced  in  con- 
creting during  freezing  weather. 

16 


RETURN      CIRCULATION  DEPARTMENT 

i*       202  Main  Libra 


642-3403 


LOAN  PERIOD  1 
4 

2 
5~ 

3 

z  

LIBRARY   USE 

This  book  is  due  before  closing  time  on  the  last  date  stamped  below 

DUE   AS  STAMPED  BELOW 

Ufifljfito  Ufrr-     - 

-•                  •.''.' 

-1^]        .. 



REC.G1R.OCT     2  '78 

FORM  NO.  DD  6A,  1 2m,  6'76         UNIVERSITY  OF  CALIFORNIA,  BERKELEY 

BERKELEY,  CA  94720 


I        Gaylamount 
Pamphlet 

Binder 
Gaylord  Bros.,  Inc. 

Stockton,  Calif. 
T.M.Reg.  U.S.  Pat.  Off 


YC  66718 


M17471 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


